Each larva

AnonymePonds and Aquariums, Let’s Investigate, Bridlington, East Yorkshire, Peter Haddock,  1997, p. 57.

Each larva constructs its tube in its own way, and while some species are quite particular about the type of material used others are less specific. The larva lives inside its tube and may carry it around with it while it searches for food. Most larvae produce a secretion that they use to cement the particles together to make them stronger.